Rainbow Electronics T89C5121 - Manual (Page 88)

88
A/T8xC5121
4164G–SCR–07/06
Reception (Mode 0) To start a reception in mode 0, write to SCON register clearing SM0, SM1 and RI bits
and setting the REN bit.
As shown in Figure 40, Clock is pulsed and the LSB (D0) is sampled on the RXD pin.
The D0 bit is then shifted into the shift register. After eight sampling, the MSB (D7) is
shifted into the shift register, and hardware asserts RI bit to indicate a completed recep-
tion. Software can then read the received byte from SBUF register.
Figure 40. Reception Waveforms (Mode 0)
Baud Rate Selection (Mode 0) In mode 0, baud rate can be either fixed or variable.
As shown in Figure 41, the selection is done using M0SRC bit in BDRCON register.
Figure 42 gives the baud rate calculation formulas for each baud rate source.
Figure 41. Baud Rate Source Selection (Mode 0)
Figure 42. Baud Rate Formulas (Mode 0)
Write to SCON
TXD
RXD
RI
D0 D1 D2 D3 D4 D5 D6 D7
Set REN, Clear RI
0
1
M0SRC
BDRCON.0
PER
CLOCK
÷ 6
To Serial Port
IBRG
CLOCK
Baud_Rate
=
6 (1-SPD) ⋅
32
⋅
(256 -BRL)
2 SMOD1 ⋅
F
PER
BRL = 256 -
6 (1-SPD) ⋅ 32 ⋅ Baud_Rate
2 SMOD1 ⋅ F
PER
a. Fixed Formula b. Variable Formula
Baud_Rate =
6
F
PER